The invention relates generally to hybrid energy systems and methods for use in connection with large, off-highway vehicles such as locomotives. In particular, the invention relates to a system and method for selectively capturing, storing, and regenerating electrical energy, such as dynamic braking energy, produced by locomotives driven by electric traction motors.
FIG. 1A is a block diagram of an exemplary prior art locomotive 100. In particular, FIG. 1A generally reflects a typical prior art diesel-electric locomotive such as, for example, the AC6000 or the AC4400, both or which are available from General Electric Transportation Systems. As illustrated in FIG. 1A, the locomotive 100 includes a diesel engine 102 driving an alternator/rectifier 104. As is generally understood in the art, the alternator/rectifier 104 provides DC electric power to an inverter 106 which converts the AC electric power to a form suitable for use by a traction motor 108 mounted on a truck below the main engine housing. One common locomotive configuration includes one inverter/traction motor pair per axle. Such a configuration results in three inverters per truck, and six inverters and traction motors per locomotive. FIG. 1A illustrates a single inverter 106 for convenience.
Strictly speaking, an inverter converts DC power to AC power. A rectifier converts AC power to DC power. The term converter is also sometimes used to refer to inverters and rectifiers. The electrical power supplied in this manner may be referred to as prime mover power (or primary electric power) and the alternator/rectifier 104 may be referred to as a source of prime mover power. In a typical AC diesel-electric locomotive application, the AC electric power from the alternator is first rectified (converted to DC). The rectified AC is thereafter inverted (e.g., using power electronics such as IGBTs or thyristors operating as pulse width modulators) to provide a suitable form of AC power for the respective traction motor 108.
As is understood in the art, traction motors 108 provide the tractive power to move locomotive 100 and any other vehicles, such as load vehicles, attached to locomotive 100. Such traction motors 108 may be AC or DC electric motors. When using DC traction motors, the output of the alternator is typically rectified to provide appropriate DC power. When using AC traction motors, the alternator output is typically rectified to DC and thereafter inverted to three-phase AC before being supplied to traction motors 108.
The traction motors 108 also provide a braking force for controlling speed or for slowing locomotive 100. This is commonly referred to as dynamic braking, and is generally understood in the art. Simply stated, when a traction motor is not needed to provide motivating force, it can be reconfigured (via power switching devices) so that the motor operates as a generator. So configured, the traction motor generates electric energy which has the effect of slowing the locomotive. In prior art locomotives, such as the locomotive illustrated in FIG. 1A, the energy generated in the dynamic braking mode is typically transferred to resistance grids 110 mounted on the locomotive housing. Thus, the dynamic braking energy is converted to heat and dissipated from the system. In other words, electric energy generated in the dynamic braking mode is typically wasted.
It should be noted that, in a typical prior art DC locomotive, the dynamic braking grids are connected to the traction motors. In a typical prior art AC locomotive, however, the dynamic braking grids are connected to the DC traction bus because each traction motor is normally connected to the bus by way of an associated inverter (see FIG. 1B). FIG. 1A generally illustrates an AC locomotive with a plurality of traction motors; a single inverter is depicted for convenience.
FIG. 1B is an electrical schematic of a typical prior art AC locomotive. It is generally known in the art to employ at least two power supply systems in such locomotives. A first system comprises the prime mover power system that provides power to the traction motors. A second system provides power for so-called auxiliary electrical systems (or simply auxiliaries). In FIG. 1B, the diesel engine (see FIG. 1A) drives the prime mover power source 104 (e.g., an alternator and rectifier), as well as any auxiliary alternators (not illustrated) used to power various auxiliary electrical subsystems such as, for example, lighting, air conditioning/heating, blower drives, radiator fan drives, control battery chargers, field exciters, and the like. The auxiliary power system may also receive power from a separate axle driven generator. Auxiliary power may also be derived from the traction alternator of prime mover power source 104.
The output of prime mover power source 104 is connected to a DC bus 122 which supplies DC power to the traction motor subsystems 124A-124F. The DC bus 122 may also be referred to as a traction bus because it carries the power used by the traction motor subsystems. As explained above, a typical prior art diesel-electric locomotive includes four or six traction motors. In FIG. 1B, each traction motor subsystem comprises an inverter (e.g., inverter 106A) and a corresponding traction motor (e.g., traction motor 108A).
During braking, the power generated by the traction motors is dissipated through a dynamic braking grid subsystem 110. As illustrated in FIG. 1A, a typical prior art dynamic braking grid includes a plurality of contactors (e.g., DB1-DB5) for switching a plurality of power resistive elements between the positive and negative rails of the DC bus 122. Each vertical grouping of resistors may be referred to as a string. One or more power grid cooling blowers (e.g., BL1 and BL2) are normally used to remove heat generated in a string due to dynamic braking.
As indicated above, prior art locomotives typically waste the energy generated from dynamic braking. Attempts to make productive use of such energy have been unsatisfactory. For example, systems that attempt to recover the heat energy for later use to drive steam turbines require the ability to heat and store large amounts of water. Such systems are not suited for recovering energy to propel the locomotive itself. Another system attempts to use energy generated by a traction motor in connection with an electrolysis cell to generate hydrogen gas for use as a supplemental fuel source. Among the disadvantages of such a system are the safe storage of the hydrogen gas and the need to carry water for the electrolysis process. Still other prior art systems fail to recapture the dynamic braking energy at all, but rather selectively engage a special generator that operates when the associated vehicle travels downhill. One of the reasons such a system is unsatisfactory is because it fails to recapture existing braking energy.
Therefore, there is a need for an improved system that captures and stores the electric energy, such as the energy generated in the dynamic braking mode, and that supplies the stored energy for later use.
In one aspect, the invention relates to a hybrid energy locomotive system for use in connection with a train. The hybrid energy locomotive system comprises a locomotive having a plurality of locomotive wheels. A locomotive traction motor is associated with one of the plurality of locomotive wheels. The locomotive traction motor has a first rotatable shaft mechanically coupled to the one of the plurality of locomotive wheels. An electric power source selectively supplies locomotive electric power to the locomotive traction motor. The locomotive traction motor is operable in response to the locomotive electric power to rotate the first rotatable shaft and to drive the one of the plurality of locomotive wheels. The locomotive traction motor further has a dynamic braking mode of operation in which the locomotive traction motor generates electrical energy in the form of electricity. An electrical energy capture system is in electrical communication with the locomotive traction motor. The electrical energy capture system selectively stores electrical energy generated in the dynamic braking mode and selectively provide secondary electric power from the stored electrical energy. The electrical energy capture system selectively supplements the locomotive electric power with the secondary electric power.
In another aspect, the invention relates to a hybrid energy locomotive system for propelling a consist on a track. The system comprises an engine. A power converter is driven by the engine and provides primary electric power. A traction bus is coupled to the power converter and carries the primary electric power. A locomotive traction system is coupled to the traction bus. The locomotive traction system has a motoring mode and a dynamic braking mode. The locomotive traction system propels the consist in response to the primary electric power in the motoring mode. The locomotive traction system generates electricity in the dynamic braking mode. An energy storage selectively captures the electricity generated by the locomotive traction system in the dynamic braking mode and selectively transfers a first portion of the captured electricity to the locomotive traction system to augment the primary electric power in the motoring mode.
In yet another aspect, the invention relates to an electrical energy capture system for use in connection with a hybrid energy locomotive system. The hybrid energy locomotive system includes a locomotive. A locomotive power source supplies primary electric power. A locomotive traction motor propels the locomotive in response to the primary electric power. The locomotive traction motor has a dynamic braking mode of operation generating electricity. The electrical energy capture system comprises an electrical energy storage device in electrical communication with the locomotive traction motor. The electrical energy storage device selectively stores a portion of the electricity generated in the dynamic braking mode and selectively provides secondary electric energy from the stored electricity.